Stereo depth cameras are well-known and are often used to measure a distance from an object. As part of the process, images of scenes are captured and measurements are taken to determine depth information. One method of determining the depth of objects in a scene from a captured image is made using triangulation.
In order to perform triangulation accurately, some calibration of the stereo depth camera is typically performed at assembly time. Calibration sets some intrinsic and extrinsic parameters of the stereo camera. Subsequent calibrations may be needed due to the system's deviation from initial calibration due to various external factors, such as temperature, humidity or barometric pressure changes, or displacement of sensing and/or projecting devices included in the system.
Stereo depth cameras are very sensitive to tiny changes in the optic elements intrinsic (e.g., Field of View or focal length) and extrinsic parameters. As a result of these changes, key depth image characteristics are biased such as absolute depth value, world coordinate y-axis yaw, scaling effects and more. Temperature variations may cause changes in the parameters, thereby causing errors in the determined depth generated by the triangulation process. Current solutions to these problems caused by temperature either ignore this source of distortion, or apply active thermal control to maintain the temperature at which the system was initially calibrated. The former approach is very weak for a real product since it implies a narrow working temperature range and the system being at the “working point” where the temperature is stable. The active thermal control allows correct operation in a wider range of temperatures, yet it consumes power, area and cost, which are all undesirable.